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Fundamental Of Disease > Pharmokinetics > Flashcards

Pharmokinetics Flashcards

1
Q

What is pharmacokinetics ?

A

Is the aspect of pharmacology which describes what the body does to the drug.

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2
Q

What are the principles of pharmacokinetics?

A

Absorbed, distributed, metabolized and excreted. (ADME)

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3
Q

What are the common oral dosage forms available?

A 
Solutions 
Suspensions
Capsules 
Tablets
Coated tablets
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4
Q

Capsules

A

hard gelatin shell consisting of a base and a tightly fitting cap. They contain diluents and fillers to ensure their stability .

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5
Q

Solutions

A

drug delivery is the fastest via solutions

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6
Q

Suspensions

A

doses can be controlled in a smaller volume and disintegration is not required for drug release.

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7
Q

What are tablets?

A

High compression of the drug

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8
Q

What is dissolution?

A

Is the rate limiting step for the drug to reach systemic circulation. Usually seen in tablets that are taken orally.

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9
Q

Coated tablets

A

Coated modification for palatability or for delay disintegration until the drug reaches the small intestines.

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10
Q

What is the rate of appearance of oral drugs in the systemic circulation?

A

Solution, suspension, capsules, tablet, coated tablets.

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11
Q

What are advantages of oral administration?

A

Cheap, no need to sterilize, compact, multiple dose bottles, automated machine produce tablets in large quantities .
Convenient, portable, no pain, easy to take
Variety, can get the oral drugs in many types, etc solution, suspension etc

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12
Q

Disadvantages of using oral drugs

A

Limited absorption of some drugs, food may affect absorption, patient compliance is necessary , drugs may be absorbed before systemic circulation, local effect

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13
Q

What is the first pass effect?

A

Drugs absorbed orally are transported to general circulation via liver.

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14
Q

Why must a doctor have patient compliance while giving oral drugs?

A

Can’t give an unconscious patient

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15
Q

Two drugs that must be given in higher amount than Iv so as to avoid the first pass effect

A

Morphine and propranolol

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16
Q

One disadvantage of using oral drugs is that it may have an local effect. Why

A

Antibiotics that are administered oral may affect the normal bacteria flora.

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17
Q

How are buccal and sublingual drugs administered?

A

Tablets are placed in the buccal pouch or under the tongue.

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18
Q

Why are sublingual drugs used?

A

For drugs that are destroyed by gastrointestinal fluids or substantial pre-synaptic degradation.

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19
Q

Examples of drugs that are administered this way (sublingually)

A

Glyceryl trinitrate (GTN) and other nitrates

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20
Q

Advantage of sublingual drugs

A

Avoid first pass effect , rapid absorption, drug stability

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21
Q

Disadvantages of sublingual administration

A

Discomfort in holding the drug under the mouths, if any swallowed the portion must be treated as an oral dose, small doses,

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22
Q

Rectal administration

A

Is given for the treatment of local conditions e.g hemorrhoids, to achieve systemic absorption , (suitable for patients who cannot take oral medication )

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23
Q

In what form are rectal administration of drugs given?

A

Form of suppository with a variety of bases ranging from cocoa butter and polyethylene derivatives., soft gelatin capsules are also used

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24
Q

Advantage of rectal administration ?

A

By pass liver, some of the veins draining the rectal lead directly to the general circulation, useful to patients who can’t take oral tablets or younger children.

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25
Q

Disadvantages of rectal

A

Erratic absorption:

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26
Q

Intravenous and intra- arterial administration

A

Used when a rapid onset of action is required

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27
Q

Slow administration of Iv and IA drugs

A

Avoids high concentration of the drug into circulation and minimizes sudden precipitation of insoluble drugs.

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28
Q

Constant administration

A

Used for acute therapy when the drug has a narrow therapeutic range and sustained blood concentration.

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29
Q

When is intra- arterial administration

A

Is considered for anti cancer drugs,

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30
Q

Advantages of intravenous

A

Rapid, total dose ( the whole dose is delivered to the blood stream), veins relatively insensitive

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31
Q

Intramuscular administration

A

Involves injection into muscle, used to administer oil based drugs, lipophillic drugs usually gain rapid access to the capillaries,

32
Q

What is a must about intramuscular administration?

A

Drugs must have a variability of water solubility . If the drug is not water soluble precipitation may occur on injection prior absorption e.g. The drug Valium ( diazepam)

33
Q

Administration of drugs to epithelial surface

A

Drugs are applied to the skin to treat skin disorder or to gain entry into systemic circulation. Maybe in the form of patches or cream formulations.

34
Q

What is the stratum Corneum?

A

Is the outermost layer of the epidermis, consisting dead cells that lack nuclei and organelles.

35
Q

Disadvantages of invenous

A

Suitable vein, may be toxic, requires trained personel and expensive

36
Q

Advantage of subcanteous

A

Can be given by patient e.g insulin absorption slow but usually complete

37
Q

Disadvantages of subcanteous

A

Can be painful ,irritant drugs can cause local tissue damage, maximum of 2 ml injection thus small doses limit use.

38
Q

Advantages of intramuscular

A

Large culex than sc, can be given

39
Q

Disadvantages of intramuscular

A

Trained personnel ISP required for injections. The site of injection will influence the absorption. Absorption is sometime erratic, especially for poorly soluble drugs. E.g. Diazepam, phenytoin

40
Q

Best site for intramuscular injection

A

Deltoid muscle

41
Q

Inhalation

A

Mainly resisted to drugs that act locally on lungs.

42
Q

How are inhalation drugs administered ?

A

By pressurized aerosols or powder inhalers e.g. Salbutamol inhaler.

43
Q

Does size of particles affect inhalation?

A

Yes, gases are efficiently absorbed but solid and liquids are excluded if larger than 20 microns and even then only 10% is absorbed.

44
Q

What is drug absorption?

A

The passage of the drug from its site of administration into the systemic circulation .

45
Q

What does drug absorption entails?

A

The passing of drugs through a barrier and membrane to reach the blood or site of infection.

46
Q

Lipid water partition

A

Ability of a drug to diffuse across membranes

47
Q

An increase in the polarity of the drug ……..

A

Decreases the lipid water partition.

48
Q

The degree of drug ionization also influences their

A

Lipid water partition coefficient

49
Q

The proportion of the total drug concentration present in either ionized or unionized state is indicated by

A

Drug dissociation constant ( Henderson Hasselbalch equation.

50
Q

The lower the PKA of an acidic drug the ………

A

Stronger the acid is

51
Q

The higher the PKA of a basic drug, ……..

A

The stronger the base

52
Q

Drugs are absorbed by one or more ways

A 
Passive diffusion
Filtration
Bulk flow 
Active transport
Facilitated diffusion
Ion pair transport 
Endocytosis
53
Q

Describe active transport

A

It energy dependent ( adenosine triphosphate ) movement of compounds across membranes , most often against their concentration gradient.
This process is facilitated by the reversible binding of the molecule to be transferred by a membrane carrier protein.

54
Q

Example of a drug that binds by active transport

A

5- fluorouracil

55
Q

Facilitated diffusion

A

Similar to active transport but no energy is needed because the passage of drugs is driven by the concentration gradient.

56
Q

Passive diffusion

A

Passage of drugs through membranes down their concentrated gradient of the unionized moiety

57
Q

A drug uses passive diffusion is

A

CNS depressant barbitol

58
Q

Describe filtration.

A

Dependent on both the existence of a pressure gradient as the driving force, the size of the drug compound and the size of the membrane pore or intracellular pores.

59
Q

Bulk flow

A

Mainly by blood flow, occurs through intercellular pores and is the main passage way of drugs across most capillary endothelial cells.

60
Q

Ion pair transport

A

Drugs which are highly ionized pair with other ions in the GIT to become neutral ions that can pass through membrane barriers.

61
Q

Endocytosis

A

Uptake of exogenous molecules in membrane vesicles by phagocytize uptake of particles and pinocytosis uptake of particles in a fluid phase.

62
Q

Absorption from the buccal cavity and sublingual.

A

Does not affect the first pass effect, rate of diffusion is faster due to the unionized form of drugs, it has a extensive network of blood vessels under the tongue facilitates rapid drug absorption.

63
Q

Absorption from the stomach

A

Epithelial lining of stomach provides a good site for absorption, low ph ionizes the drug and may effect the passage of the drug across membranes.

64
Q

Absorption from the small intestines

A

Has villi and micro villi and a complex supply of blood and lymphatic vessels into which blood is absorbed, conditions that shorten the intestinal transmit time will affect absorption e.g diarrhoea

65
Q

Absorption from the large intestines

A

Absorbs compounds that were not sufficiently absorbed by the small intestine.

66
Q

Factors that affect GIT absorption

A 
Gastric emptying time
Intestinal motility
Food
Formulation factors
Metabolism 
Blood flow in the vessels associated with the intestines .
67
Q

Factors affecting absorption after parental administrationintravenous administration

A

No significant limiting factors are seen, ensures immediate response due to direct passage of drug into blood.

68
Q

Factors affecting absorption after parental administration intramuscular and subcutaneous

A

Dependent on the quantity and composition of the connective tissue.
Dependent on the capillary density
Dependent on the rate of vascular perfusion of the area
Volume and osmolarity of the solution injected

69
Q

Factors affecting absorption through the skin

A

Outer barrier of the skin ( stratum Corneum) forms a barrier against the rapid absorption through the skin.
Enhanced by pores for the passage of drug molecules.

70
Q

Factors affecting absorption from the lung

A

Facilitated by: the large surface area of the pulmonary alveolar membranes, limited thickness of the membranes, the high. Loos flow to the alveolar region.

71
Q

Name other factors that affect absorption

A

Disease
Age
Genetics

72
Q

Disease affecting absorption

A

Comorbidity ( either the presence of one or more disorders (or diseases) in addition to a primary disease or disorder, or the effect of such additional disorders or diseases) and the use of other medications affect drug absorption. E.g. Impair their absorption e.g antacids and tetracyclines reduces the rate of absorption e.g. Anticholinergics

73
Q

Can diarrhea affect absorption of drugs from the small intestines

A

Yes.

74
Q

Age affecting absorption of drugs

A

Drug absorption is complete in an older person, although it may proceed at a slightly slower rate resulting in one or both of

Lower peak concentration
An increase in the time for the onset of drug effect

75
Q

Genetics and absorption of drugs

A

Drugs which undergo some form of metabolism before it is absorbed into systemic circulation may be affected genetic variances in cytochrome P450 isozumes.

Fundamental Of Disease (19 decks)

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